Rectangular Measuring Flumes for Lined and Earthen Channels

Abstract

Good water management in irrigated agriculture requires that irrigation water be accurately measured. Presented herein are design procedures and rating tables for modified broad‐crested weirs (which act hydraulically as long‐throated flumes) that have rectangular control sections. The ratings are presented in terms of discharge per unit width so that rectangular broad‐crested weirs of a variety of sizes can be used. This makes it easier for the designer to adapt the flume to the site rather than vice versa. These weirs or flumes can be placed in lined and unlined canals of any shape. The rating tables are presented for rectangular lined canals with given values of sill or crest height. An adjustment procedure is given to develop rating tables for other approach area and sill height combinations. The head loss across the weir required to maintain a unique head discharge relationship is also presented. Finally, a design example is given for a rectangular lined canal. With this information, a rectangular measuring flume can be designed for a wide variety of site conditions.